A number of diagnostic reagents using an antibody or a labelled antibody have recently been developed. In particular, a monoclonal antibody has been steadily extending its utility in the field of diagnosis and therapeutic drugs because of its high reaction specificity.
Many of antibodies, especially monoclonal antibodies composed of a single protein, have a unique character, which has made it difficult to obtain a stable solution thereof. Similarly to general enzyme proteins, methods of preserving antibodies include freezing, lyophilization and ammonium sulfate fractionation followed by suspension. However, these methods not only involve complicated steps not easy to carry out but require much labor for preparing an antibody solution from the preserved state on use.
Studies have thus been given to a method for preserving an antibody in the form of a solution. Proposals so far made for obtaining an antibody solution include a method of adding albumin (WO 92/01808 corresponding to EP-A-0 539 584) and a method of adding hydrolyzed egg albumin (JP-A-61-76423 corresponding to U.S. Pat. No. 4,650,772 and EP-A-0 170 983, the term "JP-A" as used herein means an "unexamined published Japanese patent application"). These methods, however, are still unsatisfactory for preparing a stabilized antibody solution.